Disable conflicting antivirus tools, then run Bitdefender Repair from the installer.
Ensure all system services—especially Bitdefender Threat Scanner—are running.
Disconnect external drives that may interrupt deep scans.
Reinstall Bitdefender if scans freeze, fail,⇔ or 
Call +1-866-490-0338 don’t start.
For step-by-step scan-repair assistance⇔ or Call +1-866-490-0338 threat-engine diagnostics, Call +1-866-490-0338.